The specific aims of this study are: 1) to test our hypothesis that cardiac factors are responsible for the "escape" of the kidneys from sodium retaining effects of mineralocorticoids, 2) to investigate possible factors modulating secretion of atrial natriuretic factor, 3) to test our hypothesis that intravenous norepinephrine inhibits vasopressin secretion largely by its effect on increasing left atrial pressure, 4) to determine hemodynamic, renal and humoral consequences of long term partial obstruction of blood flow at various intrathoracic sites, 5) to determine effects of acutely blocking vagal traffic in animals with chronic surgical denervation of the heart, 6) to determine the effects of vasopressin, angiotensin, and norepinephrine infusions on both acute and long-term blood pressure regulation, 7) to examine hemodynamic, renal, and humoral consequences of combined sinoaortic, cardiac, and pulmonary denervation, 8) to investigate possible mechanisms that enable cardiac-denervated dogs to maintain absolute blood pressure levels slightly higher than do control dogs during slow hemorrhage. These studies are health related because they deal specifically with the regulation of fluid balance and its alteration in certain physiological pathophysiological states. Derangements in fluid balance are common problems in patients with cardiovascular disease.